1. Field of the Invention
The present invention relates to a mobile station in a mobile communication system and, more particularly, to a mobile station with a short-range radio function which includes a radio section for communication with a base station and a radio section for short-range radio communication which performs communication with an apparatus with a short range, and a power consumption reducing method for the mobile station.
2. Description of the Prior Art
Recently, mobile communication systems such as a portable telephone system have become widespread.
In such a mobile communication system, radio communication is performed between a mobile station, i.e., a cell phone or radio portable terminal apparatus and a base station connected to a telephone network, thereby allowing communication with another telephone set or communication apparatus connected to the telephone network.
One of the communication schemes used by such mobile communication systems is CDMA (Code Division Multiple Access).
According to CDMA, on the transmitting side, data is spread by using one of predetermined spreading codes which differ depending on the data to be transmitted, and the spread data is transmitted. On the receiving side, the data is obtained by spreading (so-called despreading) the reception signal by using a spreading code identical to the one used on the transmitting side (to be precise, a code complex conjugate to the spreading code on the transmitting side). In such communication based on CDMA, the peak correlation value of a signal received on the receiving side is found out by shifting the despreading timing, thereby regenerating the signal transmitted from the transmitting side.
The variety of applications for recent mobile stations has increased as the number of users has increased. For example, demands have arisen for mobile stations that can transmit/receive data to/from information processing apparatuses such as a personal computer (to be referred to as a “PC” hereinafter). Such transmission/reception of data is preferably performed by radio communication in consideration of user's operability, and studies have begun to be made on interfaces for short-range radio communication.
As such short-range radio communication means, infrared communication, Bluetooth, and the like are known. By mounting such a short-range radio communication means in a mobile station like a cell phone, short-range radio communication by the mobile station is realized.
In this case, the mobile station is equipped with a radio section for the above short-range radio communication and a radio section as an essential radio section which is used to communicate with a base station. Its power consumption tends to increase more than before.
Demands, however, have arisen for smaller, lighter mobile stations which can be used for a longer period of time in a mobile communication system for cell phones or the like. For this purpose, the built-in batteries for driving mobile stations are reduced in size. To allow a mobile station to operate for a long period of time with such a compact battery, it becomes important to attain a reduction in power consumption in the mobile station.
In a conventional short-range radio communication procedure, when connection begins to be established, one unit emits a radio wave, and the other unit detects the radio wave to establish a link.
Synchronization is established by this procedure, and communication is started between the units whose connection has been established. A procedure for shifting to a state wherein power consumption is suppressed while a link is kept established when a condition occurs in which there is no data to be transmitted/received while the link is established is available as a conventional technique.
In this case, although a side on which link synchronization management is performed (to be referred to as a “master” hereinafter) can issue a transition instruction for a state shift, a side which complies with link synchronization (to be referred to as a “slave” hereinafter) can only generate a request and requires a consent from the remote unit. There has been no rule stating that when, for example, data communication is to be performed between a cell phone and a PC by using a radio interface, a specific one of the units should play the main role. That is, roles are variably assigned to such units.
In a conventional cell phone, the supply of power to circuits unnecessary for a standby state is stopped. For example, the power consumption is minimized by automatically turning off the backlight when neither input operation nor interrupt occurs for a predetermined period of time or automatically stopping setting operation when no input operation is done during the setting operation and shifting to a power saving standby state. In this manner, attempts are made to prolong the maximum battery time.
The following problems arise in the above conventional mobile station in a mobile communication system used for cell phones and the like.
First, in short-range radio communication, when a given unit operates on the side to be found in connection (slave side), it keeps emitting radio waves. That is, when a given unit operates on the side on which the short-range radio function is turned on to make a search (master side), a function of setting a time during which a search is made is prepared for the unit. If, however, a given unit operated on the side to be found, and no remote unit cannot be found, the unit keeps emitting radio waves until the user turns off the short-range radio function.
When the short-range radio function of a cell phone is to be used, the user may put the cell phone in a bag while the short-range radio function is kept on, and forgets turning off the function. As a consequence, the cell phone keeps consuming power against user's will. This may interfere with the power saving function of the cell phone and affect the standby time and speech communication time of the cell phone.
The adverse effect of radio waves on medical equipment has been brought to the fore, and radio waves in crowed places, in particular, have become a social issue. Under the circumstances, unnecessary emission of radio waves may worsen such a problem in consideration of areas where cell phones are used.
Second, the low power consumption mode prepared for conventional short-range radio communication may not always be effectively used, and a cell phone may waste power. This is because a shift to the low power consumption mode or restoration therefrom is not triggered by any specific condition, and there has been no means for making a mode shift from the cell phone side